Date: Fri, 6 Jul 2012 17:13:04 -0400 From: Rick Miller <vmiller@hostileadmin.com> To: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: Does FreeBSD start slices at head boundaries? Message-ID: <CAHzLAVEwJSMO%2BWBTAUDeYv8bLCaB-fDExRKuRqgtE52GThFHtA@mail.gmail.com> In-Reply-To: <CAHzLAVE0CahZhkKzU5=bLy5AvKsq_qgmqwAiO9BhWD3k1_uFvQ@mail.gmail.com> References: <CAHzLAVE0CahZhkKzU5=bLy5AvKsq_qgmqwAiO9BhWD3k1_uFvQ@mail.gmail.com>
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I went through this exercise to determine if there were boundary issues installing FreeBSD on disks. I concluded that FreeBSD was indeed installing at head boundaries. A colleague then pointed me to http://ivoras.net/blog/tree/2011-01-01.freebsd-on-4k-sector-drives.html which calls into question whether sysinstall and fdisk really are installing FreeBSD's slice at the 64th cylinder. Should I be concerned with this? This came about due to a scenario where Linux would start its filesystem at sector 63, right before the head boundary. On I/O intensive applications, it was common for reads/write to cross the head boundary resulting in unnecessary disk thrashing and long I/O wait times. The issue was corrected in Linux by changing the start cylinder to 2048. Some theorized that FreeBSD was vulnerable to this scenario. Thoughts/feedback? On Fri, Jul 6, 2012 at 11:09 AM, Rick Miller <vmiller@hostileadmin.com> wrote: > Hi All, > > Installing FreeBSD 8.x I select "A" at the fdisk partition editor to > use the entire disk. It creates an unused slice with offset 0 and 63 > sectors in size. Then partition 1 starts at sector 63 and utilizes > the remaining disk space. Does sysinstall's diskPartitonEditor macro > automatically start partitions at head boundaries? The reason I ask > is because I am most familiar with sector 64 being the start of a head > boundary as opposed to 63. Is my understanding incorrect? > > -- > Take care > Rick Miller -- Take care Rick Miller
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